A Roulette Chamber is an object in the game. They cost money to activate. When activated, random Items will show up in the chamber; pressing the activation button again will stop the random selection of items and give you the item currently in the chamber.
The random selection of items will gradually speed up; after enough time, the game will randomly give you an item because the selection is too fast.
Roulette Chambers drop Common, Uncommon, and Rare items, meaning that they can potentially give you great items.
A strategy with Roulette Chambers called "pause buffering" exists where you repeatedly pause the game once you activate the Roulette Chamber; once you see an item you want, you can un-pause and then immediately select the item.